The mammalian zona pellucida is an extracellular matrix comprised of three sulfated glycoproteins (ZP1, ZP2 and ZP3) that surrounds growing oocytes, ovulated eggs and embryos. The zona proteins not only have vital roles in fertilization and early development, but the genes that encode them represent a paradigm for the investigation of mechanisms of oocyte-specific gene expression. We have previously described the genetic loci of mouse Zp-2, mouse Zp-3 and human ZP3 genes and have recently characterized the human ZP2 gene and a full-length cDNA of its-transcript. Like the mouse and human ZP3 genes, the two ZP2 genes are well conserved: each is composed of 18 exons spanning approximately 12.5 kbp of DNA; the coding regions are 72% the same, and the resultant protein products are 60% identical. We have recently confirmed the presence of a second human ZP3 allele that results in a truncated protein product that is 52 amino acids shorter than the previously described allele. Both alleles are present in high frequency in human populations. Studies are currently underway to ascertain if the allele encoding the truncated protein has an adverse effect on human fertilization and early development. The spatial and temporal expression of the mouse zona pellucida genes is precisely regulated. Zp-2 and Zp-3 transcripts are expressed only in oocytes where they accumulate to high abundance during a narrow two week period of oocyte growth. The 5' flanking regions of mouse Zp- 2 and Zp-3 genes and their human homologs contain five short DNA sequences (4-12bp) that are 60-100% conserved and are approximately equidistant upstream of the TATAA box. Mutation of these five elements (I, IIA, IIB, III, IV) in ZP-luciferase constructs demonstrated that the 12bp element IV, positioned approximately 180 base pairs upstream from the TATAA box, is necessary and sufficient for high level expression from both mouse Zp-2 and Zp-3 promoters microinjected into the nucleus of 50 mu m diameter oocytes. Oligonucleotides containing the conserved element from either Zp-2 or Zp-3 form DNA-protein complexes of identical mobility in gel retardation assays using extracts from oocytes but not from other tissues. These data are consistent with the hypothesis that common factor(s) binding to the conserved element IV are involved in the coordinate expression of the oocyte-specific Zp-2 and Zp-3 zona pellucida genes.